perf top: Add --namespaces option

Since 'perf record' already have this option, let's have it for 'perf top'
as well.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Cc: Hari Bathini <hbathini@linux.vnet.ibm.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Krister Johansen <kjlx@templeofstupid.com>
Link: http://lkml.kernel.org/r/20190522053250.207156-4-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/Documentation/perf-top.txt

@@ -262,6 +262,11 @@ Default is to monitor all CPUS.
 	The number of threads to run when synthesizing events for existing processes.
 	By default, the number of threads equals to the number of online CPUs.
 
+--namespaces::
+	Record events of type PERF_RECORD_NAMESPACES and display it with the
+	'cgroup_id' sort key.
+
+
 INTERACTIVE PROMPTING KEYS
 --------------------------
 

tools/perf/builtin-top.c

@@ -1208,6 +1208,9 @@ static int __cmd_top(struct perf_top *top)
 
 	init_process_thread(top);
 
+	if (opts->record_namespaces)
+		top->tool.namespace_events = true;
+
 	ret = perf_event__synthesize_bpf_events(top->session, perf_event__process,
 						&top->session->machines.host,
 						&top->record_opts);
@@ -1500,6 +1503,8 @@ int cmd_top(int argc, const char **argv)
 	OPT_BOOLEAN(0, "force", &symbol_conf.force, "don't complain, do it"),
 	OPT_UINTEGER(0, "num-thread-synthesize", &top.nr_threads_synthesize,
 			"number of thread to run event synthesize"),
+	OPT_BOOLEAN(0, "namespaces", &opts->record_namespaces,
+		    "Record namespaces events"),
 	OPT_END()
 	};
 	struct perf_evlist *sb_evlist = NULL;